In order to increase the efficiency and the performance of gas turbine engines so as to provide increased thrust-to-weight ratios, lower emissions and improved specific fuel consumption, turbine engines are tasked to operate at higher temperatures. As the higher temperatures reach and surpass the limits of the material(s) forming the components positioned within the hot gas path of the engine, particularly components within the combustor and/or turbine section(s) of the engine, new materials must be developed.
As the engine operating temperatures have increased, new methods of cooling the high temperature alloys typically used to form hot gas path components have been developed. For example, ceramic thermal barrier coatings (TBCs) have been applied to the exterior surface of hot gas path components to reduce the heat transfer rate, to provide thermal protection to the underlying metal and to allow the component to withstand higher temperatures. In addition, cooling circuits and/or cooling holes have been introduced to provide improved cooling to hot gas path components. For example, film cooling holes are often provided in turbine blades to enhance the thermal capabilities of such components.
Moreover, ceramic matrix composite (CMC) materials have also been developed as substitutes for high temperature alloys. In many cases, CMC materials provide both temperature and density advantages over metallic materials, thereby making the materials desirable options for manufacturing high temperature, hot gas path components. Due to their high temperature capabilities, CMC-based components can often be used within a gas turbine without the need for supplying a cooling medium within and/or through the components. However, as turbine engine operating temperatures continue to increase, a need exists for providing additional cooling to CMC components. Unfortunately, by exposing the interior surface of a CMC component to a cooling medium (e.g., by using a conventional cooling design), the underlying CMC substrate is subjected to an increased thermal gradient between its interior surface and its exterior surface positioned at or adjacent to the hot gas path of the turbine engine. Such an increased thermal gradient can often result in thermal stresses that exceed the material's capabilities, thereby leading to undesirable component damage.
Accordingly, an internal thermal coating for a non-metallic composite-based component that allows for the thermal gradient between the interior and exterior surfaces of the component to be reduced and/or tailored to the specific cooling requirements of the component would be welcomed in the technology.